The purpose of this project is to investigate the regulation of liver growth and function by hormones and other factors. Since many of the pathways of amino acid utilization in liver are normally limited by the intracellular availability of these compounds, attempts are being made to characterize the transport systems for amino acids and to describe the role of hormones in the regulation of these processes. A technique which was originally developed for studies of amino acid uptake in brain has been adapted to liver for the characterization of hepatic transport systems. The uptake of C14-labeled amino acids by liver following rapid injection into the portal vein is measured relative to a simultaneously injected highly diffusable reference, tritiated water. In other studies the effects of hormones and other factors on protein turnover are being localized to specific steps in the pathways of synthesis and degradation. The isolated perfused rat liver is being used in these studies. Effects of amino acid availability, insulin, growth hormone, glucocorticoids, and fatty acid are being investigated. Studies attempting to measure the turnover of specific liver proteins are in progress. Two liver enzymes with rapid turnover rates, ornithine decarboxylase and S-adenosylmethionine decarboxylase, are being studied.